7. A Possible New Insight into Tornado-genesis at
Temperatures Inversions Aloft

8. Insights into Potential Tornado Modification or “ Control”

9. Conclusions

References

1.Introduction

Tornados, waterspouts and dust devils are sometimes
considered to be atmospheric heat engines, transforming heat energy
differences(Δ Q, ΔT)between a heat source of higher temperature
in the air at the earth’s surface and a heat sink region of lower temperature
aloft, into kinetic energy ˝ mV2 and into wind flow V and work W.

However, the initial formation of these atmospheric
whirlwinds in regions initially of small temperature differences means a
verysmall thermodynamic heat engine efficiencyand very small wind speeds, and this
conflicts with the quite sudden appearance of high winds. Some theories have
attempted an explanation by introducing additional sources of energy other than
heat, such as lightning stokes, into the vortex core[1,2] to account for this discrepancy.

Current research has concentrated, instead, on a greatly
improved understanding of the many complex dynamic details of these violent
storms provided by the availability of such tools as Doppler radarto measureinternal wind speeds in the vortices, and on numerical simulation to
model a wide range of flow possibilities. Once fully formed, these complicated
violent storms are now fairly well understood [3] but the early stage mechanism
is not.

Here, we shall examine a very rare, extremely simple, yet
violent atmospheric whirlwind which occurs under weather conditionswhich are apparently completely the opposite
to those in other whirlwinds.Tornados
and waterspouts form over warm surfaces in windy cloudy weather. This rare
whirlwind forms over cool lakes under fine, sunny,calmconditions, with the vortexarising suddenly and violently in a very small area while all else
around remains undisturbed. We shall call these special vortices“ cool-lake whirlwinds’ ( (CLW) for want of a
better name, and see if their extremely simple structure may offer clues to
understanding themore violent and
complicated storms such as tornadoes and waterspouts.

2. Vortex Motions

A Vortexinvolves organized
circulatory or rotary motion of a fluid (i.e.liquid or gas) in which the fluid motion is round and round about a
central point or centralaxis. The
swirling motion of water slowly draining from a sink or wash basin is an
example of a vortex. The flowaround the
perimeter of the basin and in themain
body of the water in the wash basinis circulating,
but it is not technically rotating.
This seems a bit contradictory, but, for example, a floating cork which has a
straight index line inscribed on its top, circulates around and round with the
water, but the orientation of the line inscribed on the cork acts much as the
needle of a compass and remains pointing in the same direction.. While the cork
and the water it is floating in certainly do circulate,they do not
themselves rotate. However in the very centre of the swirling water, if
there is no actual gap in the fluid, the motion is different ---there the water
core rotates
in a wheel-like manner so that the rotation becomes zero at the central axis.

When the flow is steady, the outer, non-rotating circulation
is described mathematically as

VT r =
Γ =constant

were Γ with dimensions of angular momentum is called
the circulation, VT is
thevelocity at any point of radius r.An
example of this type of circulatory motion is thepotential
vortex, often called a free
vortex,in which the motion can be described
by a potential velocity function φ, such that dφ/dx = V[4,5,6].

Thetrue rotational
motionin the innercore is called solid or wheel-like rotation, or sometimes aforced
vortex
or rectilinear vortex, and isdescribedmathematically as

VT/r =
ω

were ω is the rotation with the dimensions of
frequency.

Atmospheric vortices typically consist of an outer
circulatory whirl of irrotational or potential motion) enclosing a very
small inner core of solid rotation.The
presence of the solid rotational core isphysically necessary because a purecirculatory or potential vortexwould require a velocity V ofinfinity at the core where r = 0, andso, in nature, some adjustment is necessary. This problem of infinity is
avoided bya core having solid-like
rotation, since then the velocity drops to zero at the central axis where r = o
as required. The two flow systems together
are often called a Rankine combined
vortex[4,5,7,8] .

Figure 1 Rankine Combined Vortex.

The classical work on vortex
motions in fluids by Helmholtz, as extended to air motions by Rayleigh, is
described by Lamb [4] and by Prandtl and Tietjens [5].In 1934 Brunt{9}applied this vortex theory to explainthe structure of hurricanes and tornadoes. For simplicity, Brunt assumed
air to beincompressible andpostulated the vortex structure to be a
Rankine combined vortex , i.e.a forced
vortex core, surrounded by a free or potential vortex. This model was then
widely used to explain these atmospheric vortices in a general way, but
correspondence with the observed details of structure and dynamics was found to
be insufficient. For example, to explain the high wind speeds in tornadoes in
incompressible theory, a radial inflow into the vortex with conservation of
angular momentum had to be postulated.This would explain the spin-up from low speed in the outer region to
high tangential wind speeds inthe core
through conservation of angular momentum( Vr = Γ =const.) in the radialinflow. However, with inflow, it was also necessary to then postulate an
outflow ( at high levels in the atmosphere) in order to keep the process going
and avoid “filling up” the vortex.This
in turn led research off into the complex details of storm cloud dynamics.

In 1954 Abdullah [10], in an effort to improve on Brunt,
applied the theory of compressible
air flow to tornadoes which thenpermits
the transformation of internal heat energy into kinetic energy or motion.He postulated that the maximum speed would
then be the critical or Mach 1 speed given byV*= [n/n+1 ]1/2 co. where V* isequal to c*, the sonic speed, at Mach 1( approx. 301 m/s for air with n = 5). Here n is the energy partition
parameter related to the ratioof
specific heats k as n = 2/ k−1, where k = cp­/cv..

Vonnegut [1] showed later that the Abdullah sonic
velocitylimit ( M = 1) could not be reached
thermodynamically via a heat engine transformation, given the poor efficiency
of such engines and theknown
temperature differences in the atmosphere between ground and the stratosphere (
about 70˚C versus about 115˚C needed)and so he postulated an input of electrical energy from lighting strikes
in the tornado core in orderto make the
heat engine model work.[Eventually it
was determined [7, 15] by observations thattornado speeds at the ground are actually much lower, at around100 to 130 m/s, andso theenergy upgrading hypothesis was not needed].

We now proceed to examine two compressible flow models:
first the heat engine model and then an isentropicflow model.

The earlier idea
[1,2,10] that tornado wind speeds at the core were actually sonic ( i.e. about
300 m/s, 670 mph )led to great
difficulties in finding the necessary atmospheric energy source to account for
such extreme wind speeds. Later observations [7,16] that the maximum boundary
levelwinds are onlyabout 130 m/shas resulted in models that are much closer to the observations.

(b) Thevisible,
rope- like funnelof the tornadoor ‘ twister’, is not the entire swirl of
wind, but is only the visible condensed cloud of water droplets which forms
when the air in the whirl has expanded and cooled in the lower pressure which
prevails towards the center of the funnel until the relative humidity has
reached 100% .

(c) The visiblefunnel cloud emerges from the base of a
stormcloud at a height of typically
around one or two thousand meters,and
the funnel thenextends lower and lower
towards the earth’s surface.The tip of
the funnel may not reach the ground at all, and in such cases it usually
retreats back up and disappears into the parent cloud from which it
emerged.If the funnel does “ touch
down” at the ground,it suddenly broadens
in diameter and the swirling winds at the ground speed up.While the tip of the descending funnel may be
only a few meters in diameter before touch down, immediately afterwards the
base diameter typically becomes 50 to 100 meters across and may increase to
over a kilometer in severe tornados.

(d) The general air mass in which the storm forms is always
very convectively unstable with warm moist air at the ground and cool air
aloft. The parent cloud often is already, or soon becomes, a violent
thunderstorm cloud. The most severe storms are called super-cell thunderstorms.

A standard scale of tornado intensities devised by Fujita is
shown in Table 1.

One common explanation of a tornado has been that it is an atmospheric heat engine driven by
convective instability betweena warm
moist source at the ground level and the upper atmospheres at much cooler sink
temperatures, the general temperature differential in a mature tornado thus
being about 40 - 50°g C. The vorticity, i.e. the swirling or rotating motion is
usually described as having originatedfrom wind shear between interacting air streamsin the storm system [3].

The heat engine is anirreversible, non-isentropic flow, where the relationship between
velocity V, and thermodynamic quantitiesQ, and T,is given [1,6]
by:

V =[ 2 cp ΔT (ΔT/To) ]1/2
(1)

where cpis the specific heat at constant pressure (
0.244gram caloriesin air at 20C), ΔT = To −
Ti is the temperature drop from source to sink, and ΔT/To = ( ­­ To − T)/To = 1 − T/To is the
thermodynamic efficiency of the heat engine as required by the 2nd
law of thermodynamics, and which limits the amount of work that can be
extracted from any given heat input. ( The work done( dW = pdv) enters through expansion
(dv)of the air in the vortex).Table 2 shows the values of velocity V for
given values of temperature difference ΔT computed from Eqn. 1. for
atmospheric air.

Note 1.Values in red
are those corresponding to maximum observedtemperature differences in the troposphere, that is to maximum wind
speeds attainable via the heat engine thermodynamic transformation. Values in
blue correspond to the usual small temperature differences existing in the
atmosphere when vortices first form.

Figure 1. Rankine Combined Vortex

On the assumption that the flow velocities V in Table .1
apply to the tangential velocitiesVTin the vortex. (Fig.1 above )it
is clear thateven weak tornadoes with
winds of say 100 mph ( 45 m/s) will require temperature contrasts of about 15
to 20 degrees C to form. These large temperature contrasts are not evident in
the initial whirls or funnels that extend down from low lying storm cloudsonly 2000 to 3000 feet above ground so that
the heat engine fails to explain their origin.

The maximum tornadoes from super cells that have vertical
convection paths extending from ground levelto near the stratosphere do have the temperature contrast frombottom to top (source and sink) of say 50
degrees C, with the ground source inflow having a temperature of say 293
degrees and the cloud tops at say240
degrees, but this is so only after the tornado cloudis fully grownto its greatest height. The initialfunnel reaching down from the parent cloud
layer at say 2 to 3 thousand feet above ground, typically has a temperature
differencebetween cloud and ground ΔT of only about 5C degrees or so, and is
thereforeable by itself to produce
funnel winds of only 13 m/s ( 30 mph)under the thermodynamicheat
engine restrictions of small efficiency (Table 1) .

Clearly, other sources ofenergy inputmust be found, other
than purely convective instability temperature contrasts between cloud and
ground, to account for the much greater intensity of tornado winds that
actually occur. We see from Table 1 that the a heat engine model with the
temperature differentials of not more than 3 deg C that are available initially
can only account for winds of say 7.8 m/s ( 17.5 mph) instead of the 30+m/s . The
conclusion must be, that, in its initial stages, the tornado is not a
heat engine.

Once the funnel touches down at the earth’s surface
intensification occurs. The winds increase and the funnel base broadens. The
source of this additional input of energy appears related to the infiltration
of warm and moist surface air into the vortex as the drag of surface friction
unbalances the purely tangential flow and permits a partial radial inflow of
surface air. However, even, say, 3˚Cwarmer airplus2˚Cdegrees from additional condensation of water vapour to visible funnel
cloud for atotal of say , 8˚Cwill yield only21 m/s ( 47 mph) velocity versus the 50 -100
m/s observed, which would requiring a temperature differential of from 20 to 40˚C.
Again the heat engine hypothesis fails even with addition of energy from
condensation of water vapour.

We shall shortly (Section 6)explore a different thermodynamic process than the heat engine, which
does yield the observed higher wind speeds in the initial tornado stage. But
first, we explore waterspouts, dust devils and a very rare, small whirlwind
which occurs in fine weather over cool, calm water surfaces on lake and rivers.

4.0Waterspouts and DustDevilsas Heat Engines?

Waterspouts [11]have
most of the characteristics of tornadoes except that they occur only over water
and that they are less intense. Typically waterspouts are about the strength of
a category F1 tornado with surface winds of about 75 to 100 mph. They develop
from overhanging cumulus or cumulonimbus clouds and intensify as the funnel
reaches the water surface. This seems to indicate that the intensification is
due to (1) some surface frictioncausing
warm air inflow and (b) and condensation of water vapour from the moist surface
layers over the water. The surface friction over water is much less than over
land and so the surface air inflow and heat input from it aremuch less than with tornadoes, thus pointing
toa lesser intensity .

Thus far the general features of both tornadoes and
waterspouts are that they are vortices of somewhat unknown initial formation,
fuelled by an infusion oflatent heat of
condensation,but with wind speeds that
are much greater than can be explained by treating thevortex as a heat engine

Dust devils [12] are essentially small, rather weak,
atmospheric heat engines fuelled only by hot air inflow at the surface, instead
of also by condensation of water vapour. Dust devils occur under cloudless
conditions over intensely heated desert or other barren surfaces.They apparently start as random swirling
eddies, and, if intense solar surface heating and air inflow are right, they
intensify to whirlwinds of say 50 to 100 mph. ( 22 -45 m/s). They are visible
only from the swirling dust and sand that they stir up. With only one source of
heat input they are much weaker than most tornadoes.

To learn more about thedetails of atmospheric vorticesand their inner causes we now turn to an almost unknown atmospheric
whirlwind that occurs only in fine, calm, warm weather over cool waters, such
as on lakesor on calm stretches of cool
rivers.

5.0Fine weather
“Cool- lake whirlwinds”(CLW)

These rare, mysterious
whirlwinds first came vividly to personalattention on Sept.2, 1987duringa fishing expedition on a
small lake in MontTremblantProvincialPark
north of Montreal, Quebec.
My wife, Pauline, and I were in arowboat on Lacla Fourche, asmall body of water, about athird of a mile longby half that distance wide.It was afine, warm sunny morning with little or no wind. At about 11 a.m. my
wife suddenly called out in alarm at the sudden appearance out of nowhereof a small, whirling, column of mistover the waterin a small bay about 100 meters from our boat
and about 50 meters from the wooded shoreline.

The swirling mist
column was about 2 meters feet highand
1.5 meters in diameter, embedded in alargerpatch of disturbed surface
water about 8 meters in diameter. The mist column was whirling round and round
violently and emitting a hissing sound. After about 10 to 15 secondsin the same locationit disappeared as suddenly as it had formed,
leaving only a small darkened,breeze-
ruffled area on the surface of the water whichthen drifted away across the lake at about 10 km/hr toward the eastern
shore. This lake is shallow, not over 7 meters or so deep at the deepest spot.

Inspection ofthe
little bay where the whirlwindhad
erupted showed no signs of any disturbance in the water itself which was
perfectly clear right down about a meter or so to the lake bottom. Obviously
the whirl had been in the air above the water only. The lake water was cool
ataround 18 ˚C. The airtemperature was warm at about 25˚C ( 24
to 26˚C). This situation, with cool air at the surface and warmer air
above is just the reverse of the temperature stratification that occurs in
tornados and waterspouts where the air is warm at the surface and cooler aloft.

Technically stated, the usual atmospheric situation in
whirlwinds isconvective instability. This little lake
whirlwind was, however,completely stable, forming under an inversion of
temperature and with cooler air below at the surface.To a meteorologist this was all completely
mystifying.There was no wind to
initiate any swirling or vorticity
by wind shear; the sudden little vortex was violent with winds estimated at 30
to 35 m/s (68to 78 mph), there were no
storm clouds,etc. etc.

Investigation showed thatthere was only one other account in the scientific literature of a
similar phenomena occurringin North
America. That one reported a whirl of spray “ the size of a flour
barrel”suddenly appearing on a small
lake in the AdirondackMountains, N. Y Stateon a fine sunny day in May 1920[13]. It gave off a “splashing” sound and lasted a minute or so. In Europe
there were reports of a couple of somewhat similar occurrences [ 13 ].

Further investigation revealed thatBernard Bruneau, Park Warden of Mont
Tremblant Provincial Park for 24 years, had also seen suchtiny whirlwinds on the Park’s lakestwo or three times during his career, and
once on a calm stretch of a small river. All had occurred on fine, sunny, warm,
nearly windless days.

Clearly what we had seen was a very rare event.It also was so simple, meteorologically
speaking, compared to tornadoes and waterspouts, that it invited close
scientific analysis. The general situation is shown in Figures 2,3,4.

The first conclusion of the study was (1) that, if the
vortex were an atmospheric heat engine, thenthe heat source must be the warm air justabove the temperature inversion at a height
of about a meter or so above the surface of the lake; (2) the heat
differenceΔTbetween a heat source in the warm air above
the inversion and the heat sink in the core of the cortex at the lake surface
could not be more than the temperature difference between water temperature and
air temperature which was at mostabout
7˚C, and more likely was only about half that value or 3.5˚C.In that case the resulting winds from Table 1
would be only 9 to 18.5 m/s, far below the 30 to 35 m/s observed..We
cannot therefore explain this cool-lake whirlwind(CLW) as a heat engine transforming heat
energyinto wind speed.

Even adding in heat of condensation from the formation of
the column of mist in the vortex core will not make up the difference. The
liquid water content of clouds ranges from 0.2gr.to over 3 grams per m3 . Each gram
condensed out released 680 calories of heat. Therefore the temperature rise of
the air into which the vapor condenses can be calculated from the heat Q
released into the air per gram of water vapour condensed to liquid which is Q =
586 calories /gm.( or 2.454 Joules ).

In Table 3 the temperature rise in one cubic meter of air by
an injection of 586 calories of heat ( 2.454 Joules) is calculated from Q =
mass xΔT x specific heat of
air.Thus, ΔT = Q / m x 0.244 = 586
/ 1000 x 0.244 = 2.4 degrees per gram of water vapourcondensed to liquid cloud droplet form.
Neglecting several small corrections, such as for ventilationand so on, we get the following
approximatetemperature rises to be
expected from condensation: :

Table 3

Approximate
Temperature Rise ΔT Expected from

CloudCondensation in a Vortex Core

Condensed Liquid waterTemperature rise
(ΔT)/m3

0.5 g/m31.2
C

12.4
C

Therefore, condensation of the water vapour inthe inflow of moist air at the surface of the
lake into the vortex would apparently add only 1 to2.4 ˚C to the heat input, stillmuch too lowto explain winds estimatd ate 30 to 35 m/s.

Finally, we cannotexpect the inflowing air at the surface of the laketo add heat, as it does with tornadoes at
their touching down, since, in this case , the lake water is cool and the air
over it, while moist,would still be
cool. So, any inflow of surface air would be cool instead of warm and would
reduce thevortex winds instead of
increasing them..It appears then that
the heat engine modelfails to explain
the sudden violenceof these tiny rare
vortices and that someother mechanism
must be sought.

Turning from the heat
engine model, we now, instead, examine anisentropictransformation relating heatenergy in the form of temperature differences
ΔT to thekinetic energy ( ˝ mV2) and flow velocity V.Since the transformation is isentropic,
no work is done, the thermodynamic efficiency restrictionof Equation 1 does not apply, and much larger
velocitiesemerge.

The isentropic transformations ofenergy from heat intoflow velocitywith no work done, is given by [6]

V = n1/2 co
[1 −T/To]1/2
= n1/2 co [ ΔT/To]1/2(2)

.

This is derived as follows; We start with the kinematic
energy equation in terms of wave speed c, static wave speedco, temperature T, flow velocity
V, and n, the number of ways the energy of the air is divided. ( n also equals
2/ (k − 1)where k is the ratio of
specific heats cp/cv.and has the value of 1.4 for air.)As is usual in flow theory, we consider unit mass of fluid so that
m(= 1) does not appear explicitly in
the equation.

c2 = co2
− V2 /n

c2/co2
= 1 − V2 / nco2

If we now further restrict the adiabatic case to isentropicflow, we can apply the usual isentropic
relations

c2/co2
=( p/po)2/n+2 = ( ρ/ ρo)2/n = T/To
and so

T/To = 1 −
V2 /n co2 ,whence wehave Eqn. 2 above

V = n1/2 co
[1 −T/To]1/2
= n1/2 co [ ΔT/To]1/2

which gives the relationship
between flow velocity V and the temperature drop ΔT

Note 1: Values in blue are for the observed cool lake
vortex wind speeds and corresponding temperature differences. Values in red are
for the maximum observed tornado wind speeds [7,16].

It is apparent that isentropic flow velocity
transformations can account for the magnitude of thewinds arising in the CLW from very small
temperature differences in the inversion over the cool lake surface.Table 4 shows that even a temperature
differential at the inversion level of only 0.5˚C transformsor corresponds to a flow velocity of 30.4m/s or
68.1mph,while a 1˚C temperature
differential would producea wind speed
of 43 m/s ( 96.2mph).Therefore we can now explain the Lac de la
Fourche observed wind speeds of 30 to 35 m/s from the temperature difference in
thetemperature inversion over the lake
with an isentropic energy transformation.

We must note, however, that there remain certain
difficulties with the proposed isentropic explanation. Strictly speaking, such
a transformation requires that there be no heat input or output. This would
seem to rule out latent heat of condensation being involved, and yet the
visible condensation funnel is an essential fact of these vortices.Again, there is the fact that surface
temperature inversions over cool waters are very common in the atmosphere, yet
these violent little vortices are very rare.The general rule is that atmospheric processes are non-isentropic,
involving radiation heating or cooling, condensation and evaporation, and
non-isentropic turbulent exchange all of which act to overmaster the isentropic
process.

However, the sudden appearance of these rare violent
vortices is a fact, and the isentropic process can explain their sudden
appearance and their wind speeds. Their subsequent evolution, of course, almost
certainly would appear to be either non-isentropic or only
quasi-isentropic..

Finally, if this mechanism acts at one temperature inversion
in the atmosphere ( CLW), it must also be able to act at other similar
atmospheric inversions, large or small , and so we may also have also explained
the early stages of tornados and waterspoutsas well. A temperature
differential of only 10˚ C--- easily reached in the lower atmosphere-- will account for the maximum observed
wind speeds in tornadoes (Table 4).

The initial source of the tornado funnel in the lower
portion of the thunderstorm storm is now addressed.

It has been reported
that many tornado funnels originate in association with a microburst or
downburst of cool air thattakes place
under astorm cloud as a shaft of
falling rain emerges from the storm cloud. [14, 15, 16,17].This rain shaft
cools the air by evaporation and so a surge of cooler and denser air flows out
from beneath the storm cloud somewhat like a miniature shallow cold front
outflow ( Fig. 3).

Here we have a parallelphysical counterpart to the surface inversion of temperature found in
our “cool lake whirlwind ’ ( CLW) , except that now the inversion is several
thousand feet above ground at the top of the cool air dome (Fig. 3).. We
therefore propose that, just as the CLW vortex was generatedin the surface inversion over the lake,,
sotornado vortices may alsoform at the cold dome inversion generated by
falling rain from the thunderstorm cloud (Fig. 3).

Figure. 3 Tornado
forming in temperature inversion at top of precipitation-cooled air dome beneath
thunderstorm cloud

Once the tornado funnel touches the ground, the infiltration
of warm surface air would provide a second source of heat energy.Similar considerations would apply to the
case of waterspouts.

In this proposed model there are
two key phases, first, the initial phase of the tornado prior to touchdown is
not a heat engine but is an isentropic or quasi-isentropic energy
transformation process (Eqn. 2), and, second, at tornado funnel touchdown a
change in the mechanism from isentropic over to the non-isentropic heat engine
process (Eqn. 1) begins.

We must point out at this point
that the above new model, while it offers a solution to one key problem of the
thermodynamics of atmospheric vortices, is still only one aspects of the complete
picture of tornado dynamics.The new
element is a proposed solution to one current problem in all there vortices,
namely the source of the initial high wind speeds.There are, of course,many different kinds of atmospheric vortices,
gust front vortices, fair weather cumulus tornadosetc .which do not involve inversions although
all involve temperature differences.The new model also does not address the source of the initial vorticity required to start the vortex
motion; this has been quite exhaustively studied and indeed appears to now be
reasonably well understood [3]. The new isentropic energy transformation model
proposed here, then, while it appears to solve one key problem, still requires
being evaluated and integrated into the other detailed knowledge on the
structure and dynamics of these great stormsIf validated, it will obviously supply a key piece to the puzzle.

8. Insights into Potential Tornado Modification or ‘ Control’
?

The
new model points to the storm cloud’s temperature inversion area as the site of
tornado funnel formation. Here an isentropic process takes place. Anything that
interferes with the isentropic process at the inversion site would
theoretically impede tornado formation. It would therefore seem useful to study
this carefully from the point of view of physical and chemical changes which
might permit useful intervention strategies.

Again,
if condensation of water vapour does supply usable heat to the isentropic
vortexwithout disruption, then
condensation inhibitors might be of interestto tornado suppression strategies, provided that they can be employed on
a sufficiently small or local scale.

In this latter regard,
investigations into ice and condensation nucleatorssome years ago[18,19,20}] revealed that naturally
occurring organic vapours, such as terpenes and other essential oil vapours
released naturally from vegetation are very active in condensation processes.
Ammonia vapour, on the other hand,was
found to be a powerful suppressor of condensation and of cloud droplet
stability, while surfactants, such as aliphatic alcohols, and especially octal
alcohol (octanol)powerfully aided
condensation and stabilized cloud droplets against evaporation. Ammonia vapour
in milligram amounts produced observable effects of disrupting cloud growth
andstability at distances ofa kilometer or so downwind from the ground
based points of release.

Examination
of data on tornado occurrence and time trends of their frequency with respect
to concurrent changes in agricultural crop types, agricultural practices, and
environmental interventions such as pollution, might prove ofinterest.

9. Conclusions

Analysis of the very simple, cool
lake whirlwind (CLW), points solely to an isentropic thermodynamic process as
the cause.

The
initial stages of tornadoes and waterspouts can not be described as being those
of a thermodynamic or heat engine; this is because the initial atmospheric
temperature differences available are muchtoo small and the observed initial wind speeds are far too high.

An
isentropic energy transformation model does fit the initial temperature and
wind speed data of tornadoes and waterspouts; however, any ordinary inflow of heat would contradict the
isentropic process, so that a purelyinternal energy transformation
must also be postulated. This also requires an internal isentropic flow for any latent heat released from
condensation of water vapour in the incipient tornado funnel.

We therefore conclude that the
isentropic process does play a key role in tornado-genesis, but that the
details of the flow mechanism remain to be understood.